In recent years, companies have adopted document management systems to convert paper documents into digital documents, and have promoted the re-use of these documents. In an early document management system, a paper document is scanned as an image by a scanner, and that image is registered and saved. Recently, however, digital documents created by personal computers have become widespread, and such digital documents can be registered and saved.
Also, in recent years, it is possible to extract arbitrary pages from a plurality of registered digital documents, to compress and archive these pages, and to bind these pages like a binder to form a single digital document (compressed archive file). Such files will also be referred to as digital binders hereinafter. Such digital binders allow editing of internal files, and changing of individual files.
Conventional digital binders, however, suffer the following problems. In the conventional digital binder, in order to acquire the contents of the compressed digital binder, a series of processes for retrieving the entire digital binder onto a memory or as a file, and decompressing that binder are required. However, when data to be frequently accessed by the user is included in the digital binder, the user must decompress that data every time he or she accesses the data. For this reason, a very long time is required to process digital documents bound by the digital binder.
Upon processing the digital binder, a program must assure a large work memory area in advance on a main or sub storage device so as to decompress the compressed digital documents.
Such digital binders can be registered in a database that manages digital binders. The user can execute an edit process, save process, search process, and the like for digital binders registered in the database. One of the important functions of this database is a check-out/check-in function. In some cases, a plurality of users can access an arbitrary digital binder. In such environment, when a given user begins to user that digital binder, he or she can declare the right of edit to other users by setting the digital binder in a check-out state using the check-out function. In this manner, using the check-out function, a single digital binder can be prevented from being opened and edited by a plurality of users at the same time. Upon completion of such edit process, the check-out state is canceled using the check-in function, and a change in digital binder made by the user is reflected on the digital binder on the database. After the check-out state is canceled, other users can edit that digital binder.
In such digital binder management method, however, when a given digital binder is checked out, that digital binder is copied, and the copy of the digital binder undergoes an edit process and the like.
Since the check-out process is made for each digital binder, all digital documents contained in each digital binder can be accessed by acquiring the copy of that digital binder, thus posing a security problem.
Also, illicit copies are easily produced.